1. Field of the Invention
The present invention relates to a coating line system for smoothly repairing a coating defect on a coated workpiece such as any of various coated components of an automobile, and a method of repairing a coating defect in such a coating line system.
2. Description of the Prior Art
When a coating defect is discovered on an automobile bumper in a bumper coating line during an inspection process, it has heretofore been customary to rub the defective coating surface with sandpaper or the like to remove the defective coating layer from the bumper, and then coat the ground bumper surface again in the bumper coating line. The conventional repairing process has been disadvantageous because both newly coated and recoated workpieces are present in the coating line, resulting in a low overall coating rate. Another problem is that since even those portions of bumpers which do not need to be coated again are recoated, the entire repairing process is tedious and time-consuming, and consumes a large amount of coating solution.
In many coating lines, a workpiece is coated in a coating booth and thereafter dried in a drying furnace down-stream of the coating booth. According to Japanese laid-open patent publication No. 5-50006, for example, a setting booth is located between a coating booth and a drying furnace. After a coated workpiece is dried with air in the setting booth, the coated workpiece is charged into the drying furnace in which it is baked and dried.
As disclosed in Japanese laid-open patent publication No. 5-50006, the coating booth has its interior space divided into a vertical array of compartments or chambers including a dynamic pressure chamber, a static pressure chamber, a coating chamber, and a trapping chamber that are arranged downwardly in the order named. Air is supplied from a supply duct connected to an upper wall of the coating booth into the dynamic pressure chamber, from which the air is introduced at a constant rate into the static pressure chamber through a punched metal sheet lying between the dynamic pressure chamber and the static pressure chamber. The air introduced into the static pressure chamber is then supplied to the coating chamber through a filter extending between the static pressure chamber and the coating chamber. The air flowing into the coating chamber is free of dust particles because dust particles are filtered out by the filter. While flowing in the coating chamber, the air collects a mist of unused coating solution which remains suspended in the coating chamber. The air with the collected mist of coating solution is then introduced into the trapping chamber in which the mist of coating solution is trapped by trapping water flowing in the trapping chamber.
The coating booth which is compartmented into the various chambers including the trapping chamber that has a circulatory passage for the trapping water is large in size and expensive to manufacture.
Japanese laid-open utility model publication No. 60-188995 discloses a drying furnace. The disclosed drying furnace has a workpiece conveyor extending in the longitudinal direction of a furnace housing for moving a carriage with a workpiece mounted thereon. Hot air supply ducts are disposed one on each side of the workpiece conveyor and positioned respectively in lower side positions in the furnace housing, and a hot air discharge duct is connected to an upper wall of the furnace housing. Hot air supplied from the hot air supply ducts is applied to dry coated surfaces of the workpiece on the carriage, and is then discharged from the hot air discharge duct.
When the workpiece moving in the furnace housing is brought to an emergency stop due to some trouble or the rate of operation of the conveyor is lowered, more hot air than is necessary is applied to the coated surfaces of the workpiece. At this time, the workpiece is heated to a temperature higher than a predetermined allowable temperature, and hence tends to be distorted, elongated, or otherwise damaged. Furthermore, it requires a large-scale system for supplying and discharging hot air to set the workpiece to the predetermined temperature within a short period of time.
There have been demands for a coating line system of relatively simple structure which is capable of easily and efficiently repairing coating defects on coated workpieces, and a method of repairing a coating defect in such a coating line system.